Accomplished fantasy/SF writer Card ( The Memory of Earth ) has turned his autobiographical short story ``Lost Boys'' into an intriguing demi-mainstream novel. Here the Card family has been transmuted into the Fletchers, devout Mormons with three children and another on the way. A job offer from a South Carolina computer software company motivates Step Fletcher to move there; he is still seeking the financial success that once seemed assured via a computer game he invented. Unsettled by the move, their eldest son, Stevie, has trouble adjusting in school and becomes introverted, taking refuge with imaginary friends. Meanwhile, the Fletchers meet new people in their Mormon ward (including a religious hysteric), Step is the victim of malicious office politics and the family is beset by constant money troubles and worries about Stevie. Their concern escalates when young boys begin to disappear from the community, especially since the missing boys bear the names of Stevie's imaginary companions. Most of this absorbing novel has the pull of family drama with an over-layer of rising suspense, until Card switches genres and introduces half a dozen ghosts into the narrative. A cruel, if redemptive, experience for the Fletchers ensues. Though some readers may find the fantastic plot elements jarring, Card's easy and natural prose goes a long way toward authenticating the supernatural intrusion. (Oct.)